Sinewave 3KVA Inverter Using SG3525 Circuit

In this post we discuss a simple 2kva inverter circuit using the IC SG3525, which can be easily upgraded to sinewave 3kva by increasing the mosfet and the transformer specs. The circuit was designed by Mr. Anas Ahmad.

Component Set Up and Wiring

The explanation regarding the proposed SG3525 2kva inverter circuit can be understood from the following discussion:

hello swagatam, i constructed the following 3kva 24V inverter modified sine wave (i used 20 mosfet with resistor attached to each, moreover i used center tap transformer and i used SG3525 for oscillator).. now i want to convert it to pure sine wave, please how can i do that?

Basic Schematic

My Reply:

Hello Anas,

first try the basic set up as explained in this SG3525 inverter article, if everything goes well, after that you can try connecting more mosfets in parallel.....

the inverter shown in the above daigram is a basic square wave design, in order to convert it to sine wave you must follow the steps explained below The mosfet gate/resistor ends must be configured with a BJT stage and the 555 IC PWM should be connected as indicated in the following diagram:

Regarding Connecting parallel mosfets

ok, i have 20 mosfet(10 on lead A, 10 on lead B), so i must attached 2 BJT to each mosfet, that's 40 BJT, and likewise i must connect only 2 BJT coming out from PWM in parallel to the 40 BJT? Sorry am novice just trying to pick up.

Answer:
No, each emitter junction of the respective BJT pair will hold 10 mosfets...therefore you will need only 4 BJTs in all....

Using BJTs as Buffers

1. ok if i may get you right, since you said 4 BJTs, 2 on lead A, 2 on lead B, THEN another 2 BJT from the output of PWM, right?
2. am using 24 volt battery hope no any modification to the BJT collector terminal to the battery?
3. i have to use variable resistor From oscillator to control the input voltage to the mosfet, but i don't know how i will go about the voltage that will go to the base of the BJT in this case, what will i do so that i want end up blow up the BJT?

Yes, NPN/PNP BJTs for the buffer stage, and two NPN with the PWM driver.
24V will not harm the BJT buffers, but make sure to use a 7812 for stepping it down to 12V for the SG3525 and the IC 555 stages.

Reader Interactions

Comments

Thanks… Back .. Saw your modification.. 1. My transformer is already designed as 24v 3kv..but I realized you said transformer must be rated lower than the battery voltage for getting optimum voltage at the output.

if my battery is 24V i can use an 18-0-18V ..in this case that I already got 24v trans and will use 24v battery..so what will I do?

Ok thanks1. You said 24v battery should use 18-0-18 trafo which is 46v trafo? So I realized my trafo is 12-0-12v trafo which is 24v center tap trafo ..does that mean that I can use it on 24v battery since is 12-0-12v?

2. From the initial design your oscillator sg3525 design is different from mine..cz mine has variable resistor to control output volt and another variable to control the freq..but on yours it seems is not like that..so should I adapt your design? Is it best for the full some wave like you did in the old circuit?

3. The pin 10 on your old design was used for something that I don't understand..while mine is going to be used for protection..can you explain more? Am thinking that should used your oscillator circuit than mine.

Hello sir, im trying to make an inverter.i have 10-0-10v/10A transformer, im using SG3525 IC and two sets of IRF3205×3mosfets.When i connect the battery shortcircuit happened.please design a circuit for me with these specifications

Hello, the short circuit could be happening due to some fault in your circuit connections which should be checked and rectified….you can refer to any standard sg3525 design and compare it with your design to troubleshoot the fault.

Very great idea,i kwon it is not easy to put up an idea like this. Thanks sir. Can you please send me your e-mail address. I am a begginer,and i may need your help in some aspects when building an inverter.

Sir,i am building a 3kva square wave 24vdc as input and 230vac output inverter. I want to add an ac volt meter to show the output 230vac but i don't know how. Can you please help me out. The volt meter i am using is an analog one . I took it from an old stabilizer.

yes you can use a ferrite core, however for that you might need a two stage inverter, one for converting the battery volatge to a high frequency above 50kHz for creating 300V DC through a ferrite core, and then back to 220V AC at 50 Hz you can see the following example for the deatils

From the schematic, I see a BJT buffer stage at the H-bridge Processor (after the output of the 220v terminals of the ferrite core trafo, )

-The IC (IR 2153) is not available at present in my location and have thus opted to use this Schematic (which uses SG 3525) in this article of yours.

1>Since this SG 3525 schematic has a BJT buffer prior to the Primary Turns of the Trafo, will it be okay if ignore one BJT buffer?

2>Which BJT buffer Can be ignored without affecting the desired output? The one at the Primary Side of the Trafo or the one at the H-bridge processor?

3>Do you have any other schematic of a simple H-bridge Processor which has few components? (Coz the H-Bridge processor in the link you provided is kinda long)

4 >From this schematic (the SG 3525 oscillator in this article ) it is evident that the output from the proposed ferrite core trafo Will be Approximately sine waves which is what we intended, the only issue will be with the massive numbers of Frequencies (>10Khz).Do you have any other simple tentative means of lowering those huge frequencies to the normal 50/60Hz without using a H-bridge processor?

5>What appliances will be limited to work/operate with the 220v ac output (of a ferrite core inverter constructed without a H-bridge Processor) which is approximately Pure sine wave but at Kilohertz Levels?

6>If I am to Scale up an INVETER ~say to 10KW, do the mosfets of the H-Bridge Processor have to be increased?

If the PWM stages is included then I am afraid the BJT stage must be included with the full bridge stage in order to keep the mosfet as safe as possible from the PWM spikes, and enable the use of low value resistors with the gates.

Normally it should be high frequency 330V first and then 50Hz low frequency conversion using a full bridge, therefore if you are intending to use the above SG3525 design along with a full bridge then I would recommend you transfer the PWM BJT stage at the low side mosfets of the full bridge.

I had some follow up questions based on the above schematic (i could have asked in the appropriate article but the comment/reply section was absent,..is it because It was a dead modified link???..any way that's not very crucial)

1)The SG3525 oscillator schematic recommended in this full bridge circuit was always associated with centre tapped trafos, For clarity's sake, can you confirm to me if the trafo in the associated H-Bridge circuit is "NOT CENTER TAPPED"?

2)Does the word "Full Bridge" in the title "sg3525-full-bridge-inverter-circuit" mean that the output of the trafo will be of 50/60Hz?

I am humbled by your readiness to help everyone in time, whenever a Question or issue is raised.

Thanks Benedict for your questions, the discussion will not only help by website it will also help the many needy readers visiting this website, I appreciate it a lot.

when I said "replace' I meant replacing the entire stage, not the IC specifically. You can replace the 2153 stage entirely and put a SG3525 stage with its outputs reestablished with the bases of the NPN/PNP buffer stage, the same can be done using a 4047 IC stage, meaning any oscillator can be employed, 2153 is not compulsory.

The comment/reply section will be present in every article, and therefore it should be available in the linked full bridge article too…sometimes this blogger website behaves abnormally and therefore you might seen the slot missing, but I think you should be able to see on some other time, because I can see it from here, it is available.

OK, here are answers to your further questions:

1) An H-bridge or a full bridge configuration is specifically developed to eliminate the center tapped transformer and to increase the efficiency 2 folds, therefore here too a single winding transformer will be required between the mosfets

2) No it is not related to frequency, any desired frequency can be used, frequency is not a relevant parameter.

Hello sir than-xx for tutorial …i have made this circuit i get output when i connected 2amp 12-0-12 transformer to output of circuit but one problem is there when i connected 500watt transformer at the end output that time ic555 get dammaged please give me the solution .

Hello Ravindra, the Ic 555 has no chance of getting damaged, because it is powered from a 7812 IC and the pin#3 is connected through 10k resistors…I think you should check the connections again, or may be your IC is not of good quality, better change it with a god quality one….also check and make sure the output from the 7812 is indeed 12V.

OK no problem, and the reply is the same from my side, you must be able to implement it correctly in the software to get the correct results…by the way it has been already tested by me practically so need of any simulation…anyway simulators are just a waste of time.

Hi Swag, am very happy to see your sacrificial effort towards helping others through this site. God bless you. I have some questions concerning the circuit diagram1. can i replace the SG3525 with SG35242. instead of using 20 mosfet with power dissipation of 150 watts (3000va/20 = 150va), can i use a mosfet with power dissipation of 300 watts{3000va/10 =300va} so that i will use 10 mosfets in total(5 mosfets on leg A and 5 mosfets on leg B)3. if i change or reduce the 24v to 12v can i obtain a 1kva pure sine wave inverter using the circuit diagram. if i can't obtain a 1kva from 12v battery, please help me with a pure sine wave inverter design using 12v battery. Thanks

the answer to your first and second questions are yes, you can go ahead with the mentioned steps.

However if you intend to use 12V then the current requirement will be huge, around 1000/12 = 83 amps, which might require a monstrous transformer, using a 24V supply will make it 50% smaller…therefore higher voltage is recommended in order to reduce the size of the trafo and the associated wiring proportionately. sinewave can be possible with a 12V battery also, that's not an issue.

thanxx for reply ….sir please tell me what is the logic(analog) behind this circuit? i want to connect over voltage protection and low voltage protection circuit with this inverter circuit and battery discharge auto cut off circuit ….where i get knwoledge about it pls prefer me any book or link

Hello,Swagatam I hope to continue with the building of the Sg3525 pure sine inverter circuit, not to abandon it.From my colleagues comments they are doing well left me alone. So please apart from the main circuit the chopping off circuit being the Ne555 circuit in the design are there any other that I must add before getting my 50hz at output. Be cause in some of your design you use 2(ne555)configured in addition with 741 circuit before piloting the 2bgt and the MOSFETs gate. Your designs are like exams tests, am a semi skilled electronic so please don't leave out.I want to remain with your blog.For God's sake help me alone if am to add something else. Thanks for your endurance,we know you are always snowed down but you still care for everyone, be strong.

Hello Anthony, the IC 555 PWM stage explained in the above article will be enough for achieving a sine wave equivalent output, the opamp version is won't be necessary…so if you wish to build a SG3525 based sine wave inverter then you can try the design which is shown in the above article, if you have specific questions, you may feel free to ask them here

Hello mentor goodmorning, I used the design of Mr Ainsworth Lynch 2016, around the ne555 circuit he used 15volts zened diode with pin#2,6&7. I changed it to 1N4118,so am using 10 nanon at pin#5 and 100 nanon at pin#2,6 to have 240hz at pin#3 of the I.c. I built the main circuit perfectly and its outputs I got 5volts d.c each with metre reading and 50hz each with the frequency. But when I connect the P.W.M circuit it divides the voltage halfway giving 2.4volts and frequency 150hz which is unstable often as I said in my early comments. My challenges maybe is still with the selecting of the true capacitors,from my layman methods I used different strategic in vain but same attitude. How can I handle this problem? I don't have oscilloscope and don't know the use and how to come by one and the cost.

Hello Anthony, if your IC555 circuit produces constant PWM, then the output will also replicate the same and it cannot be unstable….I have expressed this many times even to the other readers that meters often give incorrect and misleading readings especially when high frequency with harmonics are involved, if you want accurate reading then you must employ an oscilloscope, or better build the entire circuit and test it with a practical load.

If you are a newcomer then i would advise you to start from the scratch and try to learn everything associated with this concept first, or alternatively you may take the help of an expert in your area during the construction.

the waveform for your circuit also should be quite similar to what is shown in the following article

Hello sir, I sincerely appreciate you for the effort you put in to help electronics hobbyists like me. I have some questions sir.
1. I’ll like to add an overload protection circuit with auto-cutoff or auto-power-off feature to the above inverter circuit. Could you help me with such a circuit? I’ll really appreciate it.
2. If I’m using a transformer with an extra winding for charging at the secondary (220V) side which gives about (14.5-0-14.5) at the primary (12-0-12) side when connected to 220V a.c mains, can I use it to charge the inverter battery through the MOSFETS without requiring an extra circuit for charging? I’m using IRF150N.
Thanks in anticipation.

Thanks a lot for the reply sir. What I actually meant was the addition of another circuit entirely to the existing one to power off the inverter when an overload is sensed at the transfo output. I still want to utilize the opamp that powers off the inverter when battery is low (as in your 3525 sine wave inverter article).
Also, do I need to add any components to the schematic to enable the MOSFETs charge the battery without harming the circuit, or do I need an entire schematic for the battery charging?

for the battery charger section, in addition to a charging circuit you will also need a DPDT switch which will need to be manually switched whenever the trafo is used in the charging mode. when the charging is completed the switch can be reverted in the inverter mode.

First Good new is then Question.
I have successfully built pure sine inverter using KA3525 and IRF540n and really getting 100% pure sine wave on oscilloscope. But i have made some modifications in design to get 100% pure sine wave. I have to add battery protection, no load detection, overload protection and twin battery charger modules. Will share it with you once completed this project.

I have a question, I have connected 100 Ohm 1/2 watt resistor to each mosfet gate. I am afraid of resistor wattage value. Can you please tell me what wattage should be of gate resistor.

The gate resistor can be 1/4watt because mosfet gates do not work with current, they work with voltage, if it was a BJT then wattage would be a concern but not for mosfets, so it’s fine to use 1/4 watt, if possible reduce the value to 10 ohma 1/4 watt

Hello Mr Swagatam for your valued help. Honestly your work is priceless. I’ve been following this thread and have now managed to draw up a circuit diagram for the 3kva sinewave inveter. I wanted to ask if you can post a complete parts list as recommended by you. I also need to if I can use IRFPS3810 for the power stage. I’m left with building of the inveter after ordering the said parts.
Thank you.

Hello Sir
Thank you again for your undying help Sir. I have managed to get the parts for the inveter and managed to connect these in a circuit.

Unfortunately Sir my inveter for the square wave stage is not responding accordingly. I’m using a transformer; 6-0-6 which gives 12V end to end, a 12V/14Ah battery, two IRF 3205, 25W bulb as a load. When I connect the battery the load only lights up when I removed the terminal from the battery but at the same time giving off a spark, and this happens only for a second. I’ve designed my oscillator stage as above described and i hope you can help trouuble shoot the problem. I’m wondering if the electrolytic cap at pin #8 is not of the right value because it’s 22uf instead of 33uf or should I also play around with the two presets. I’m afraid I’ve no testing means whatsoever at my disposal, it’s just by trial and error sir.

I’ve sent a labelled picture to your gmail account sir. I hope your find time and check it and reply here for the sake of others who might encounter the same challenge.

Thanks Mthokozisi, the above design was sent by another reader after testing it successfully. The only modification he wanted was the sinewave conversion, and I explained him how to do it in the above article.

As you can see there are many connections and wiring involved and a slightest mistake can cause problsm, so you will have to investigate why your circuit is not working, and for that you will have to understand the functioning of the iC pinouts thoroughly otherqwise you may keep struggling to identify the fault.

any circuit must be always built stagewise, here too before connecting the mosfets or the PWM, you must first confirm whether or not the IC is generating the required 50/60Hz pulses across its output pinouts?? If not then certainly you might have made a mistake in the connections or your IC may be malfunctioning.

alternatively you can checkout other similar SG3525 configurations from other online sites and try one of them which may be easier to build

Ok Sir I think I’ll try your configuration of the SG3525 as it looks straight forward, I’ll have to leave out the conductor because I don’t have as of now andi hope it won’t be an issue. I’ll come back to the comments section.

hello sir,
am planning to bulid this 3kva inverter (although i have few idea about electronics). my questions are
1. is the schematic above pure sine wave inverter ?
2. can this power loads like tv, microwaves fans, etc ?
3. which online international merchant can i get all this component?
4. do you recomend me to build this first, or try your other simple inverters before this.
i will appreciate your quick reply sir,
thanks.

Thanks for the fastest reply sir, now my last questions are
1. Can I convert that to pure sine wave, if yes how pls?
2. If no, can I use this at home as a source of power for live! Without any problem of noise {maybe signal collision} (I read the advantage of pure wave over modified sine wave is noise).
3. Do you recommend me to use this as source of income, because if I could achieve this, am planning to start selling off to some shops that depends on electricity. (They will use it on refrigerator)
God bless you once again sir.

Mr swag happy new year,i just fund your blog and i think i would like to build this inverter using the sg 3525, but i would like more informating on the ic 555 wich one is Vcc,voltage,ground,reset and so on please i will wait to hear from you sir,thank.

Please Swag,
I would like you to help me, I build an inverter using IC GS3525 successfully with auto change-over by means of a relay but the problem is that, the oscillator switching time is slow by seconds, when city power go off, my Computer also it goes off. So this affect the computer.
Please Swag help me to solve this problem.

Hi Swag,
I have changed the capacitor from 16v , 10urf to 10v,22urf but there no change the delay is still big it takes off the computer.
secondly, also i followed the IC SG3525 Pinout description,It indicate that pin # 7 can be used to determine DEAD time on both outputs of the IC So I changed from 470 ohoms (1/4w) Resistor to 4.7 ohoms still no change. So please guide me, the values of the Resistors and capacitors you expect to work those places ; i.e pin#7 and 8 .
thanks.

Hi Swag,
Thank you for helping all electronic hobbyist without rejecting beginners.
sir my problem is still about the inverter which l build using sg3525 It ls working fine BUT Isolating computer because of dead time yet l changed the capacitor 0.1uf there is no difference the delay is still big which does not support computer sensitivity when city power cut off. Therefore, engineer Swag, lf the chance of fixing this problem is not near ,
Please sir, can you design for me “A good working circuit cool in running like sg3525 with a wide range of power source 8-35v) which can solve my problem
long live SWAG.

Hi Moses, it is not the dead time that needs to be checked, it is the soft start timing, which is related with pin#8. You can reduce the pin#8 capacitor to 0.1uF…by the way how have you implemented the automatic changeover from mains to battery??